1. rest completely for a week2. Identify which exercises cause him direct pain.3. avoid/replace those exercises when he returns to training4. If the above doesnt work and the pain remains, off to the physio for rehab advice and proper diagnosis.

i had tendinitis in my knees, i found out after a long hiatus from fitness. I tried to get back in shape and just running around killed my knees.

What I used, and what I recommend for your father to use on a consistent basis, is a dietary supplement made from dehydrated milk. I know it sounds weird but it actually worked well, its called Micosamine and it's specifically for promoting flexibility as well as joint function.

Here are some studies i dug up if you wanted to know about the thing you might put into your body, LOL.